1. Field of the Invention
The present invention relates to print-control methods, printing systems, and print-control apparatuses.
2. Description of the Related Art
Inkjet printers that form dots by ejecting ink onto a medium (paper, cloth, OHP sheet, etc.) are known as printing apparatuses for printing an image (hereinafter, these are referred simply as “printers”). Such printers perform a dot formation operation by for example ejecting ink while moving a plurality of nozzles in a movement direction. Raster lines are formed on the medium in the movement direction of the nozzles in this dot formation operation. The printers also perform a carrying operation of carrying the paper in an intersecting direction that intersects the movement direction of the nozzles (hereinafter referred to as the “carrying direction”). When the printer repeatedly performs the dot formation operation and the carrying operation, a plurality of raster lines that are parallel in the carrying direction are printed on the medium. A print-control apparatus, for example, controls this printing operation. A computer on which a printer driver is installed corresponds to such a print-control apparatus.
With this type of printer, the ejection characteristics of the ink droplets, such as the ink droplet amount and its travel direction, vary for each nozzle. This variation in ejection properties is undesirable because it can cause darkness non-uniformities in the printed image. Accordingly, in conventional printers, a correction value is set for each nozzle, and the amount of ink is set based on those correction values that have been set (for example, see JP 2-54676A). That is, output property coefficients that indicate the properties of the ink ejection amount for each nozzle are stored in a head property register. Those output property coefficients are then used when ink droplets are ejected in order to prevent darkness non-uniformities in the printed image.
Such a printer corrects the ejection amount for each nozzle but does not take into consideration darkness non-uniformities that are caused by bending in the path of travel of the ink droplets and darkness non-uniformities that are caused by carrying discrepancies of the medium. Such darkness non-uniformities occur due to the pitch between adjacent raster lines being smaller or larger than a specific pitch, and with conventional printers cannot be fixed easily. This is because such darkness non-uniformities occur due to the combination of the nozzles that are responsible for adjacent raster lines.